[2.x] fix: Runner should fail on JDK < 17 for sbt 2.x by eureka928 · Pull Request #8825 · sbt/sbt

eureka928 · 2026-02-27T04:53:04Z

Summary

When sbt 2.x is run with JDK 8, the runner now prints a clear error message instead of the confusing "server was not detected" error.

Problem

Running sbt -Dsbt.version=2.0.0-RC9 with JDK 8 produces:

[info] server was not detected. starting an instance
[error] failed to connect to server

This happens because for sbt 2.x, isRunNativeClient() returns true by default, which skips the JDK version check entirely. The native client then fails with a confusing error.

Solution

Detect the JDK version before the native client decision in all three runner entry points, and require JDK 17+ when sbt major version >= 2:

Bash runner (sbt): Added checkJava17ForSbt2() function, moved java_version detection before the native client branch
Windows batch (sbt.bat): Updated :checkjava to parse sbt version and require 17 for sbt 2.x, moved call before native client branch
Windows native launcher (sbtw/Main.scala): Extracted Runner.minimumJdkVersion() helper, moved JDK check before shouldRunNativeClient

Users now see:

[error] sbt 2.x requires JDK 17 or above, but you have JDK 8

Test results

Bash function test (7 cases, all pass):

=== sbt 2.x with JDK 8 -> should fail ===
[error] sbt 2.x requires JDK 17 or above, but you have JDK 8
BLOCKED (expected)

=== sbt 2.x with JDK 17 -> should pass ===
PASS (expected)

=== sbt 1.x with JDK 8 -> should pass ===
PASS (expected)

=== sbt 2.x with JDK 11 -> should fail ===
[error] sbt 2.x requires JDK 17 or above, but you have JDK 11
BLOCKED (expected)

=== sbt 2.x with JDK 21 -> should pass ===
PASS (expected)

=== no sbt version -> should pass (no check) ===
PASS (expected)

=== init_sbt_version fallback ===
[error] sbt 2.x requires JDK 17 or above, but you have JDK 8
BLOCKED (expected)

sbtw unit tests (`sbt sbtwProj/test`):

[info] sbtw.RunnerSpec
[info] - minimumJdkVersion should require JDK 17 for sbt 2.x
[info] - minimumJdkVersion should require JDK 17 for sbt 2.x snapshot
[info] - minimumJdkVersion should require JDK 8 for sbt 1.x
[info] - minimumJdkVersion should require JDK 8 when version is absent
[info] - minimumJdkVersion should require JDK 17 for future sbt 3.x
[info] Passed: Total 5, Failed 0, Errors 0, Passed 5

Verification

sbt sbtwProj/compile passes
sbt sbtwProj/test — 5/5 pass
sbt sbtwProj/scalafmtCheck passes
Bash checkJava17ForSbt2 tested manually — 7/7 cases pass

**Problem** Running sbt 2.x with JDK 8 produces a confusing "server was not detected" error because the JDK version check only required JDK 8+ and only ran in the non-native-client path. **Solution** Move java_version detection before the native client decision and add checkJava17ForSbt2 that requires JDK 17+ when sbt major version >= 2. Fixes sbt#8813

Move JDK version check before native client decision in sbtw and require JDK 17+ when build.properties declares sbt 2.x.

Move checkjava before native client decision in sbt.bat and require JDK 17+ when build.properties declares sbt 2.x.

Extract JDK version check logic into Runner.minimumJdkVersion for testability. Add RunnerSpec with tests for sbt 1.x, 2.x, and 3.x version detection.

eureka928 · 2026-02-27T04:54:04Z

Manual test proof (before vs after)

Before (develop branch) — JDK 8 + sbt 2.x:

The sbt script's isRunNativeClient() returns true for sbt 2.x, skipping the JDK version check entirely. The native client then fails:

$ sbt -Dsbt.version=2.0.0-RC9  # with JDK 8
[info] server was not detected. starting an instance
[error] failed to connect to server

After (this branch) — JDK 8 + sbt 2.x:

The new checkJava17ForSbt2 runs before the native client decision and catches it immediately:

$ sbt -Dsbt.version=2.0.0-RC9  # with JDK 8
[error] sbt 2.x requires JDK 17 or above, but you have JDK 8

After — JDK 17 + sbt 2.x (normal operation):

$ sbt -Dsbt.version=2.0.0-RC9  # with JDK 17
(check passes, sbt proceeds normally)

After — JDK 8 + sbt 1.x (backward compatible):

$ sbt -Dsbt.version=1.10.7  # with JDK 8
(check passes, sbt proceeds normally — sbt 1.x only requires JDK 8)

Note: JDK 8 is not installed on my test machine, so the bash function was tested by simulating java_version=8 and build_props_sbt_version=2.0.0-RC9 against the extracted checkJava17ForSbt2() function (7 test cases, all pass). The sbtw Runner.minimumJdkVersion logic is covered by 5 unit tests.

eed3si9n · 2026-02-27T05:18:55Z

FYI - we have fake java script in https://github.com/sbt/sbt/blob/develop/launcher-package/integration-test/bin/java, which returns 'openjdk version "1.8.0_212"'. You might need to bump that to JDK 17.

eureka928 · 2026-02-27T05:22:50Z

Thanks @eed3si9n — good catch. I've bumped the fake java script from JDK 8 to JDK 17 in 52c79d7 so the citest2 (sbt 2.x) integration tests won't be blocked by the new JDK version check.

The fake java script used by launcher integration tests reported JDK 8. Since sbt 2.x now requires JDK 17+, the citest2 (sbt 2.x) integration tests would fail with the new JDK version check.

Instead of silently ignoring --rt-ext-dir (which causes sbt.bat to mkdir on an empty string), properly simulate JDK 9+ behavior by creating a temp directory with java9-rt-ext- prefix and a dummy rt.jar inside it.

eureka928 · 2026-02-27T13:42:08Z

Happy Friday @eed3si9n
This is ready to go as well😉
Thank you for review and merging

eed3si9n

Thanks!

**Problem** Running sbt 2.x with JDK 8 produces a confusing "server was not detected" error because the JDK version check only required JDK 8+ and only ran in the non-native-client path. **Solution** Move java_version detection before the native client decision and add checkJava17ForSbt2 that requires JDK 17+ when sbt major version >= 2. Fixes sbt#8813

**Problem** Running sbt 2.x with JDK 8 produces a confusing "server was not detected" error because the JDK version check only required JDK 8+ and only ran in the non-native-client path. **Solution** Move java_version detection before the native client decision and add checkJava17ForSbt2 that requires JDK 17+ when sbt major version >= 2. Fixes sbt#8813 * [2.x] fix: Fail early when sbt 2.x is run with JDK < 17 (sbtw) Move JDK version check before native client decision in sbtw and require JDK 17+ when build.properties declares sbt 2.x. * [2.x] fix: Fail early when sbt 2.x is run with JDK < 17 (sbt.bat) Move checkjava before native client decision in sbt.bat and require JDK 17+ when build.properties declares sbt 2.x. * [2.x] test: Add minimumJdkVersion helper and unit tests for sbtw Extract JDK version check logic into Runner.minimumJdkVersion for testability. Add RunnerSpec with tests for sbt 1.x, 2.x, and 3.x version detection. * [2.x] test: Bump fake java to JDK 17 for integration tests The fake java script used by launcher integration tests reported JDK 8. Since sbt 2.x now requires JDK 17+, the citest2 (sbt 2.x) integration tests would fail with the new JDK version check. * Simulate JDK 9+ rt.jar handling in fake java script Instead of silently ignoring --rt-ext-dir (which causes sbt.bat to mkdir on an empty string), properly simulate JDK 9+ behavior by creating a temp directory with java9-rt-ext- prefix and a dummy rt.jar inside it.

**Problem** Running sbt 2.x with JDK 8 produces a confusing "server was not detected" error because the JDK version check only required JDK 8+ and only ran in the non-native-client path. **Solution** Move java_version detection before the native client decision and add checkJava17ForSbt2 that requires JDK 17+ when sbt major version >= 2. Fixes #8813 * [2.x] fix: Fail early when sbt 2.x is run with JDK < 17 (sbtw) Move JDK version check before native client decision in sbtw and require JDK 17+ when build.properties declares sbt 2.x. * [2.x] fix: Fail early when sbt 2.x is run with JDK < 17 (sbt.bat) Move checkjava before native client decision in sbt.bat and require JDK 17+ when build.properties declares sbt 2.x. * [2.x] test: Add minimumJdkVersion helper and unit tests for sbtw Extract JDK version check logic into Runner.minimumJdkVersion for testability. Add RunnerSpec with tests for sbt 1.x, 2.x, and 3.x version detection. * [2.x] test: Bump fake java to JDK 17 for integration tests The fake java script used by launcher integration tests reported JDK 8. Since sbt 2.x now requires JDK 17+, the citest2 (sbt 2.x) integration tests would fail with the new JDK version check. * Simulate JDK 9+ rt.jar handling in fake java script Instead of silently ignoring --rt-ext-dir (which causes sbt.bat to mkdir on an empty string), properly simulate JDK 9+ behavior by creating a temp directory with java9-rt-ext- prefix and a dummy rt.jar inside it. Co-authored-by: Dream <[email protected]>

**Problem** Running sbt 2.x with JDK 8 produces a confusing "server was not detected" error because the JDK version check only required JDK 8+ and only ran in the non-native-client path. **Solution** Move java_version detection before the native client decision and add checkJava17ForSbt2 that requires JDK 17+ when sbt major version >= 2. Fixes #8813 Co-authored-by: Dream <[email protected]>

eureka928 added 4 commits February 27, 2026 05:32

[2.x] fix: Fail early when sbt 2.x is run with JDK < 17 (sbtw)

ba0ca88

Move JDK version check before native client decision in sbtw and require JDK 17+ when build.properties declares sbt 2.x.

[2.x] fix: Fail early when sbt 2.x is run with JDK < 17 (sbt.bat)

efa3c68

Move checkjava before native client decision in sbt.bat and require JDK 17+ when build.properties declares sbt 2.x.

[2.x] test: Add minimumJdkVersion helper and unit tests for sbtw

671acf5

Extract JDK version check logic into Runner.minimumJdkVersion for testability. Add RunnerSpec with tests for sbt 1.x, 2.x, and 3.x version detection.

[2.x] test: Bump fake java to JDK 17 for integration tests

800e9cb

The fake java script used by launcher integration tests reported JDK 8. Since sbt 2.x now requires JDK 17+, the citest2 (sbt 2.x) integration tests would fail with the new JDK version check.

eureka928 force-pushed the fix/jdk17-check-sbt2-8813 branch from 52c79d7 to 800e9cb Compare February 27, 2026 05:44

Simulate JDK 9+ rt.jar handling in fake java script

4991af5

Instead of silently ignoring --rt-ext-dir (which causes sbt.bat to mkdir on an empty string), properly simulate JDK 9+ behavior by creating a temp directory with java9-rt-ext- prefix and a dummy rt.jar inside it.

eed3si9n added 2.x backport candidate 1.x backport candidate labels Feb 27, 2026

eed3si9n approved these changes Feb 27, 2026

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eed3si9n merged commit 28d877f into sbt:develop Feb 27, 2026
15 checks passed

eed3si9n mentioned this pull request Mar 1, 2026

[1.x] bport: Runner should fail on JDK < 17 for sbt 2.x #8854

Merged

eed3si9n mentioned this pull request Mar 1, 2026

[2.0.x] bport: Runner should fail on JDK < 17 for sbt 2.x (#8825) #8855

Merged

eureka928 mentioned this pull request Mar 2, 2026

[2.x] "server was not detected" (runner should fail on JDK 8) #8813

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[2.x] fix: Runner should fail on JDK < 17 for sbt 2.x#8825

[2.x] fix: Runner should fail on JDK < 17 for sbt 2.x#8825
eed3si9n merged 6 commits intosbt:developfrom
eureka928:fix/jdk17-check-sbt2-8813

eureka928 commented Feb 27, 2026

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eureka928 commented Feb 27, 2026

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eed3si9n commented Feb 27, 2026

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eureka928 commented Feb 27, 2026

Summary

Problem

Solution

Test results

Bash function test (7 cases, all pass):

sbtw unit tests (sbt sbtwProj/test):

Verification

Uh oh!

eureka928 commented Feb 27, 2026

Manual test proof (before vs after)

Before (develop branch) — JDK 8 + sbt 2.x:

After (this branch) — JDK 8 + sbt 2.x:

After — JDK 17 + sbt 2.x (normal operation):

After — JDK 8 + sbt 1.x (backward compatible):

Uh oh!

eed3si9n commented Feb 27, 2026

Uh oh!

eureka928 commented Feb 27, 2026

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eureka928 commented Feb 27, 2026

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sbtw unit tests (`sbt sbtwProj/test`):